2026-02-05スタンフォード大学
A map showing continental mantle earthquakes across the globe. | Axel Wang
＜関連情報＞
- https://news.stanford.edu/stories/2026/02/study-global-map-mantle-earthquakes-preparedness-risk-assessment
- https://sustainability.stanford.edu/news/study-reveals-extent-rare-earthquakes-deep-layer-below-earths-crust
- https://www.science.org/doi/10.1126/science.adz4367
- https://www.sciencedirect.com/science/article/abs/pii/S0012821X21003447
世界の大陸マントル地震 Continental mantle earthquakes of the world
Shiqi Wang and Simon L. Klemperer
Science Published:5 Feb 2026
DOI:https://doi.org/10.1126/science.adz4367
Editor’s summary
Deep earthquakes tend to cluster near subduction zones and can be explained by plate motions; however, this is not so for continental mantle earthquakes, which are hard to explain and even harder to detect. Wang and Klemperer developed a method that uses regional seismic waves and their relative amplitudes in the context of nearby recorded crustal earthquakes. Applied globally, this approach has detected more than 400 continental mantle earthquakes since 1990. These mantle earthquakes generally occur in areas that also have crustal earthquakes, but regional distributions suggest that mantle earthquakes occur under a wider range of tectonic and thermal conditions than previously thought. —Angela Hessler
Abstract
Continental mantle earthquakes (CMEs) and their implications for the rheological structure of continents have fascinated geophysicists for more than half a century. Existence of these earthquakes is no longer debated, but their identification remains sparse across the globe. Comparing the Sn and Lg seismic wave amplitude ratio (Sn/Lg) of an earthquake with that of nearby earthquakes distinguishes CMEs and, unlike previous methods, can be applied globally. We present a global distribution of CMEs that extends well beyond previous individual detections and areas of speculation. CME occurrence is widespread globally yet patterned regionally, reflecting local lithospheric structure and tectonic history. Our results highlight the value of CMEs for understanding continents and global tectonics.
ラブ波の通常モードは上部マントル地震と地殻地震を区別する：チベットにおけるシミュレーションと実証 Love-wave normal modes discriminate between upper-mantle and crustal earthquakes: Simulation and demonstration in Tibet
Shiqi Wang, Simon L. Klemperer
Earth and Planetary Science Letters Available online: 21 July 2021
DOI:https://doi.org/10.1016/j.epsl.2021.117089
Highlights
- Earthquakes above or below Moho excite stronger Lg or Sn amplitudes, respectively.
- We demonstrate this Sn/Lg effect theoretically, via synthetics, and with real data.
- We confirm three previously-known south-Tibet deep earthquakes have sub-Moho foci.
- We identify two new NW-Tibet sub-Moho earthquakes directly below lower-crustal events.
- Fully seismogenic lithosphere implies India underplates Tibet to the Altyn Tagh fault.
Abstract
We discriminate upper-mantle earthquakes from crustal earthquakes based on the amplitude ratio of seismic waves Sn and Lg (‘Sn/Lg’), a prominent feature of regional seismograms that is visible to the naked eye. Crucially, our new method uses only the waveforms of the candidate earthquake, unlike previous methods to identify upper-mantle earthquakes that introduce potentially large errors by comparing hypocentral depths with independent measures of crustal thickness. Our synthetics show that the Love-wave higher modes that form individual Sn and Lg Airy phases on the transverse component are preferentially excited when the source is respectively below or above the Moho. We use three previously recognized mantle events from southern Tibet to validate our new approach and show that focal mechanism, intrinsic attenuation, geometrical spreading etc., can be ignored to first order. We then identify two new upper-mantle earthquakes in NW Tibet where, previously, only lower-crustal events had been reliably demonstrated, thereby showing this NW-Tibet lithosphere is seismogenic at all depths i.e. that upper-mantle and lower-crustal earthquakes co-exist. Our method has potential for expanding the global catalog of continental earthquakes reliably determined to be close above or close below the Moho.
